1894.] 



VISCERAL AXAT05IY OP ORKITHOBHTNCHUS. 



721 



" he." But between the apparent end o£ this flap and the muscle 

 " e " was a slight thickening, ligamentous in texture, of the inter- 

 ventricular wall of the heart. I hardly noticed this until I had 

 examined the second heart. In the latter tlie septal jlap of the 



Pig. 3. 



r-sp 



Heart of Omithorhynckus, with right ventricle opened. 

 sp, septal flap of valve. | a, a', severed muscles of outer valve-flap. 



right auriculo-ventricular valve ivas completely developed. It was 

 tied down to the interventricular septum by two slight papillary 

 muscles, which, however, did not, as in the case of the other half 

 of the valve, at all invade the tendinous tissue of the valve. They 

 were attached to its edge merely by the tendons. This septal 

 half of the valve lay close to the interventricular waU, as, indeed, is 

 generally the case among mammals ; in the first of the two hearts 

 it was so little detached from the ventricular wall as almost to 

 suggest a case of cardiac disease rather than a normal structure. 

 But the state of affaii's in the second heart showed plainly how it 

 was necessary to interpret the first heart. It will be noticed that 

 my observations agree entirely with those of Gregenbaur, particu- 

 larly in the case of the first heart, in which (to quote from Prof. 

 Lankester's translation of Gregenbaur's paper) " no trabeculse pass 

 Pkoc. Zool. Soc— 1894, No. XLVIII. 48 



